The prior method of determining the concentration of non-aggregated platelets and the fraction that are discs, in platelet-rich plasma to be transfused to a patient, is to invasively remove a sample from the transfusion bag and then (1) dilute an aliquot to a high degree (3000:1), which is then counted on an automatic cell counter to give platelet concentration, and (2) to observe visually in a phase microscope a portion of the undiluted sample and subjectively determine (count) the fraction of the platelets that are discs. These combined procedures require the use of at least two expensive pieces of equipment by a highly skilled technician and require at least 30 minutes per sample. Thus, it is a very costly procedure. Furthermore, one is not allowed to routinely sample a transfusion product due to the risk of contamination. For these reasons platelet-rich plasma is usually not checked prior to transfusion to insure good quality, and the quality of transfused platelets is often very poor. There is a definite need for an improved method and apparatus which allows accurate quantitation of the platelet concentration and of the percentage or fraction that are discs, without risk of contamination, using a moderately priced instrument for a short period, for example, about 2 minutes, and being within the range of skill of a relatively inexperienced aid or technician, and thus to enable routine assessment of all bags of platelet-rich plasma which are to be employed for transfusion. Such an improved method and apparatus would enable usage of supplies of platelets which are beginning to show signs of slight functional deterioration but which are still useful, whereas patients would not be transfused with platelets found to be non-functional and useless.
A preliminary search of the prior art revealed the following U.S. patents of interest:
Hogg, U.S. Pat. No. 3,893,766 PA1 Breddin et al, U.S. Pat. No. 4,066,360 PA1 Frazer et al, U.S. Pat. No. 4,070,113 PA1 Kent et al, U.S. Pat. No. 4,135,818 PA1 Carlson et al, U.S. Pat. No. 4,139,303 PA1 Ehrly, U.S. Pat. No. 4,201,470 PA1 Stohr, U.S. Pat. No. 4,243,318 PA1 Haina et al, U.S. Pat. No. 4,252,438